Active matrix liquid crystal display device and liquid crystal material

ABSTRACT

An active matrix liquid crystal display device is provided, in which an after image remaining after removing an application of a direct current voltage is suppressed. The active matrix liquid crystal display device has a liquid crystal layer containing a liquid crystal molecule having negative dielectric anisotropy and a dopant having a dissociative group.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid crystal display device,and more particularly, it relates to an active matrix liquid crystaldisplay device of a so-called in-plane switching type.

[0003] 2. Description of the Related Art

[0004] A liquid crystal display realizes display in such a manner thatan electric field is applied to liquid crystal molecules in a liquidcrystal layer sandwiched by a pair of substrates to change theorientation direction of the liquid crystal, so as to cause opticalchange of the liquid crystal layer.

[0005] The conventional active matrix liquid crystal display device isrepresented by a twisted nematic (TN) display system, in which thedirection of the application of the electric field to the liquid crystalis set in the direction perpendicular to the substrate plane thatsandwiches the liquid crystal, and the display is realized by utilizingthe optical rotation of the liquid crystal layer.

[0006] On the other hand, a liquid crystal display device of a in-planeswitching (IPS) system has been proposed in JP-B-63-21907, U.S. Pat. No.4,345,249, WO 91/10936 and JP-A-6-160878, in which a comb electrode isused, and the direction of the electric field applied to the liquidcrystal is set in the direction parallel to the substrate plane, wherebythe display is realized by utilizing the birefringence of the liquidcrystal.

[0007] The in-plane switching system has advantages, such as a wideviewing angle and a low load capacitance, in comparison to theconventional TN system, and is being rapidly developed in recent yearsas a new active matrix liquid crystal display device that supersedingthe TN system.

[0008] In the IPS system, the in-plane switching can be more perfectlyrealized in the case where the liquid crystal has negative dielectricanisotropy in comparison to the case of a liquid crystal having positivedielectric anisotropy, as demonstrated in J. of Appl. Phys., vol. 82,No. 4, pp. 528-535 (1997) by M. Oh-e, M. Yoneya and K. Kondo. The liquidcrystal having negative dielectric anisotropy has a dielectric constantin the short axis direction of the liquid crystal molecule that islarger than the dielectric constant in the long axis directionperpendicular thereto, and the liquid crystal having positive dielectricanisotropy has a dielectric constant in the short axis direction of theliquid crystal molecule that is smaller than the dielectric constant inthe long axis direction perpendicular thereto.

[0009] The perfect realization of the in-plane switching completesenhancement of the viewing angle of the liquid crystal display deviceincluding halftone. Therefore, the liquid crystal having negativedielectric anisotropy is preferred as a liquid crystal used in the IPSsystem from the foregoing standpoint.

[0010] The IPS system employs an opaque metallic comb electrode in astripe form provided on an inner surface of one of the pair ofelectrodes.

[0011] In recent years, a modified system of the IPS system has beenproposed in that the comb electrode is formed with a transparentelectroconductive substance, such as ITO (indium tin oxide), instead ofthe opaque metallic electrode, and is arranged at a shorter intervalthan the conventional IPS system, and a liquid crystal material havingnegative dielectric anisotropy, whereby the entire liquid crystalpresent above the transparent comb electrode can be subjected toorientation change only with an electric field formed at the peripheryof the comb electrode, so as to improve the transmittance and theopening ratio.

[0012] Literatures relating to the foregoing proposal include AsiaDisplay 1998, pp. 371-374, by S. H. Lee, S. L. Lee and H. Y. Kim and SIDdigest 1999, pp. 202-205, by S. H. Lee, H. Y. Kim and T. Y. Eom.

SUMMARY OF THE INVENTION

[0013] The foregoing literatures report that in the IPS system combiningthe liquid crystal material having negative dielectric anisotropy andthe short interval transparent comb electrode, such transmittance thatis close to the TN system can be realized with maintaining such wideviewing angle characteristics that is equivalent to the IPS system.

[0014] It has been known in a liquid crystal display device that in thecase where a liquid crystal driving voltage waveform having a directcurrent voltage superposed is applied to a liquid crystal layer, thedirect current voltage (direct current offset voltage) remains in theliquid crystal layer even when the direct current voltage is removed.

[0015] As discussed in S. Matsumoto, Ekishou Display Gijutu (LiquidCrystal Display Technique), published by Sangyo Tosho Co., Ltd., Chap.2, pp. 70-73, the application of the driving voltage waveform having adirect current voltage superposed to the liquid crystal layer may occurin an active matrix liquid crystal display device in an ordinary liquidcrystal operation due to the structure of the active driving element ofthe liquid crystal display device, and it is difficult to completelyprevent the superposing phenomenon of a direct current voltage whengradation display is conducted. The phenomenon is common to both the TNsystem and the IPS system conventionally employed.

[0016] The remaining direct current voltage affects the brightness inliquid crystal display devices of both the TN system and the IPS system,and difference in brightness is caused between a part applied with thedirect current voltage and a part not applied therewith or between partshaving different intensities of the applied direct current voltage.

[0017] Therefore, in the case, for example, where texts or graphics aredisplayed under ordinary driving conditions for a long period of time,such a phenomenon occurs that the texts or graphics that have beendisplayed are displayed for a certain period after turning off thedisplay.

[0018] As a result, uniformity of display is impaired. Such a phenomenonis called as an after image of a liquid crystal display device, which isgradually decreased in intensity with the lapse of time after formationthereof and is finally disappeared, but there are cases where a periodof 30 minutes or more is required to disappear upon viewing with thenaked eye.

[0019] As a mechanism that when a direct current voltage is applied, thedirect current offset voltage remains in a liquid crystal layer, a modelexplaining by behavior of ions in the liquid crystal layer in theconventional TN system as an example has been proposed in Shingaku Gihou(Technical Research Report of Institute of Electronics, Information andCommunication Engineers), EID96-89, pp. 29-34 (1997-01).

[0020] According to the model, a direct current voltage charged in anoriented film and absorption of ions on an orientation film fordirecting the liquid crystal are considered as factors of the directcurrent voltage remaining in the liquid crystal layer, and it sums upthat the remanence of the direct current voltage for several minutes iscaused by charging and relaxation of the orientation film, and theremanence of the direct current voltage for a longer period is caused byabsorption of ions on the orientation film.

[0021] The IPS system suffers more frequent occurrence of the afterimage than the TN system. In the TN system, only liquid crystalorientation controlling layers and a liquid crystal layer are presentbetween a pixel electrode and a counter electrode, and an electric fieldis applied to the pixel electrode, the liquid crystal orientationcontrolling layer, the liquid crystal layer, the liquid crystalorientation controlling layer and the counter electrode in this order.

[0022] On the other hand, the IPS system has an insulating layer inaddition to the liquid crystal layer and the liquid crystal orientationcontrolling layers between the pixel electrode and the counterelectrode, and the electric field is applied to the pixel electrode, theliquid crystal orientation controlling layer, the liquid crystal layer,the liquid crystal orientation controlling layer, the insulating layerand the counter electrode in this order.

[0023] That is, because charging and relaxation of the orientation filmsand the insulating film are considered while only the orientation filmis considered for the remanence of the direct current voltage in the TNsystem, the after image is liable to occur in the IPS system as comparedto the TN system.

[0024] In TN system, the after image is liable to occur when aninsulating layer is arranged on the pixel electrode or the counterelectrode to sandwich the insulating layer between pixel electrode andthe counter electrode, to which the electric field is applied.

[0025] However, the occurrence of the after image can be suppressed byopening holes on the insulating film at positions above the pixelelectrode and the counter electrode, so as to apply the electric fieldon the pixel electrode, the liquid crystal orientation controllinglayer, the liquid crystal layer, the liquid crystal orientationcontrolling layer and the counter electrode in this order.

[0026] JP-A-7-159786 proposes a method for suppressing the remanencephenomenon of the direct current voltage caused by charging andrelaxation of the orientation film by optimizing the dielectric constantand the specific resistance of the orientation film and the liquidcrystal. In order to suppress the after image by accelerating thecharging and relaxation of the orientation film and the insulating film,it is effective that the liquid crystal has a lower specific resistance.

[0027] The specific resistance of the liquid crystal can be decreased byadding a substance that decreases the specific resistance of the liquidcrystal. For example, JP-A-11-302652 proposes that the specificresistance of a liquid crystal can be adjusted by adding an oxidativecompound to the liquid crystal.

[0028] The after image causes no problem when a liquid crystalcontaining the oxidative compound is used in the IPS system using aliquid crystal material having positive dielectric anisotropy and theIPS system combining a liquid crystal material having positivedielectric anisotropy and a short interval transparent comb electrode.

[0029] However, the occurrence of the after image cannot be completelyavoided by using the oxidative compound in the IPS system using a liquidcrystal material having negative dielectric anisotropy and the IPSsystem combining a liquid crystal material having negative dielectricanisotropy and a short interval transparent comb electrode.

[0030] The oxidative compound has a molecular structure that is similarto the liquid crystal material having positive dielectric anisotropy.That is, one of the both ends in the long axis of the molecule is formedwith a group having polarity other than a group having no polarity orextremely weak polarity, such as an alkyl group or an alkoxy group.

[0031] The other of the ends is formed with a group having highpolarity, such as a cyano group or a fluorine-containing group, and itis polarized in the longer axis of the molecule rather than the shorteraxis of the molecule.

[0032] The liquid crystal molecule having positive dielectric anisotropyis also polarized in the longer axis of the molecule rather than theshorter axis of the molecule. In other words, the liquid crystalmaterial having positive dielectric anisotropy and the oxidativecompound agree to each other in the molecular axis direction and thepolarizing direction. It is therefore considered that the remainingdirect current voltage can be effectively relaxed.

[0033] However, in the case of the liquid crystal material havingnegative dielectric anisotropy, the both ends in the longer axisdirection of the molecule are formed with a group having no polarity orextremely weak polarity, such as an alkyl group or an alkoxy group, andone end in the shorter axis of the molecule is formed with a grouphaving high polarity, such as a cyano group and a fluorine-containinggroup. Therefore, it is polarized in the shorter axis of the moleculerather than the longer axis of the molecule.

[0034] As described in the foregoing, the liquid crystal material havingnegative dielectric anisotropy does not agree to the oxidative compound,which has a molecular structure that is similar to the liquid crystalmaterial having positive dielectric anisotropy, in the molecular axisdirection and the polarizing direction. Therefore, it is considered thatthe remaining direct current voltage cannot be effectively relaxed.

[0035] The invention has been developed to solve the foregoing problemsassociated with the conventional art.

[0036] An object of the invention is to provide an active matrix liquidcrystal display device of an IPS system that is difficult to cause astate of ununiform display remaining after application of a directcurrent voltage, i.e., an after image, in an IPS system using a liquidcrystal material having negative dielectric anisotropy and an IPS systemcombining a liquid crystal material having negative dielectricanisotropy and a short interval transparent comb electrode.

[0037] Another object of the invention is to provide an active matrixliquid crystal display device of an IPS system that is difficult tocause an after image by adding a dissociative dopant and modifying theshape of the electrode even in the case where a liquid crystal materialhaving positive dielectric anisotropy.

[0038] In order to accomplish the objects, the invention relates to anactive matrix liquid crystal display device comprising

[0039] a pair of substrates;

[0040] a liquid crystal layer sandwiched by said pair of substrates;

[0041] orientation films defining an orientation direction of a liquidcrystal molecule of said liquid crystal layer, said orientation filmsbeing arranged between said pair of substrates and said liquid crystallayer; and

[0042] a pixel electrode and a counter electrode applying a voltage tosaid liquid crystal layer,

[0043] said liquid crystal molecule of said liquid crystal layer havingnegative dielectric anisotropy, and said liquid crystal layer containinga dopant having a dissociative group.

[0044] A liquid crystal display device causing less after image can beprovided.

[0045] In order to accomplish the objects, the invention relates to anactive matrix liquid crystal display device comprising a pair ofsubstrates, at least one of which is transparent; liquid crystalorientation controlling layers formed on surfaces of the pair ofsubstrates facing each other; a liquid crystal layer comprising a liquidcrystal composition having negative dielectric anisotropy arrangedbetween the pair of substrate to make in contact with the liquid crystalorientation controlling layers (orientation films); a pixel electrodeand a counter electrode formed on one of the pair of substrates throughan insulating film; and an active element connected to the pixelelectrode and the counter electrode, the liquid crystal layer containinga dopant having a dissociative group only in a shorter axis direction ofthe molecule and having an alkyl group or an alkoxy group on both endsof a molecular axis direction.

[0046] According to the liquid crystal display device, the liquidcrystal material having negative dielectric anisotropy and the dopanthaving a dissociative group only in a shorter axis direction of themolecule agree to each other in the molecular axis direction and thepolarizing direction.

[0047] Therefore, the remaining direct current voltage can beeffectively relaxed, and a liquid crystal display device causing lessafter image can be provided.

[0048] The dopant having a dissociative group referred herein means anacidic dissociative substance or a basic dissociative substance, or inother words, a substance generating an H⁺ ion through dissociation byitself in a polar solvent or generating an OH⁻ ion through a reactionwith water.

[0049] Specific examples thereof include a carboxylic acid (including ananhydride thereof), an amide, an amine and an alcohol. When thesesubstances are added to a liquid crystal, the ion concentration in theliquid crystal is increased, so as to decrease the specific resistance.

[0050] It is preferred that the pixel electrode and the counterelectrode are transparent electrode formed with a transparent electrode,such as ITO, and electric insulation between the pixel electrode and thecounter electrode is maintained by a transparent insulating film. Forexample, the pixel electrode may be a short interval transparent combelectrode, and the counter electrode may be a solid electrode. Thetransparent insulating film may be constituted, for example, with IZO,silicon nitride, titanium oxide, silicon oxide and a mixture thereof.

[0051] When the dopant has the following structure represented by thegeneral formula (I), it can effectively relax the remaining directcurrent voltage, so as to provide a liquid crystal display deviceexhibiting less after image. The dopant having the following structurehas a molecular structure that is similar to a liquid crystal materialhaving negative dielectric anisotropy.

[0052] That is, both ends in the longer axis direction of the moleculeare formed with a group having polarity other than a group having nopolarity or extremely weak polarity, such as an alkyl group or an alkoxygroup.

[0053] Since it has a dissociative group in the shorter axis directionof the molecule, it is strongly polarized in the shorter axis directionof the molecule.

[0054] The liquid crystal molecule having negative dielectric anisotropyis also polarized in the shorter axis direction of the molecule ratherthan the longer axis direction of the molecule.

[0055] The liquid crystal material having negative dielectric anisotropyand the dopant having the following structure agree to each other in themolecular axis and the polarizing direction.

[0056] Accordingly, the remaining direct current voltage can beeffectively relaxed.

[0057] wherein Y₁ represents any one of —COOH, —CONH₂, —NH₂, —OH, —NHRor —NR₂; Y₂ represents anyone of hydrogen, —F, —CN, —COOH, —CONH, —NH₂or —OH; Y₃ represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂or —OH; Y₄ represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂or —OH; X₁ represents any one of a single bond, —CO—O—, —O—CO—, —COCH₂—,—CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one ofa single bond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—, —CH₂O—, —OCH₂—,—CH₂—CH₂— or —CH═C—; A₁ represents any one of a single bond, a phenylenegroup or a cyclohexylene group; A₂ represents any one of a single bond,a phenylene group or a cyclohexylene group; R₁ represents any one of analkyl group or an alkoxy group; and R₂ represents any one of an alkylgroup or an alkoxy group.

[0058] Furthermore, when the dopant has the following structurerepresented by the general formula (II), it can more effectively relaxthe remaining direct current voltage, so as to provide a liquid crystaldisplay device exhibiting less after image. The dopant having thefollowing structure has a molecular structure that is further similar toa liquid crystal material having negative dielectric anisotropy. Thatis, both ends in the longer axis direction of the molecule are formedwith a group having polarity other than a group having no polarity orextremely weak polarity, such as an alkyl group or an alkoxy group.

[0059] In this application, single bond means direct connection. In caseX1 is single bond, for example, A1 connect directly to benzenestructure.

[0060] Since it has a highly dissociative group or a group having highpolarity at one end of the shorter axis direction of the molecule, it isstrongly polarized in the shorter axis direction of the molecule. Sincethe liquid crystal material having negative dielectric anisotropy has agroup having high polarity, such as a cyano group or afluorine-containing group, at one end of the shorter axis direction ofthe molecule, it is polarized in the shorter axis direction of themolecule rather than the longer axis direction of the molecule.

[0061] The liquid crystal material having negative dielectric anisotropyand the dopant having the following structure agree to each other in themolecular axis and the polarizing direction. Accordingly, the remainingdirect current voltage can be effectively relaxed.

[0062] wherein Y₁represents any one of —COOH, —CONH₂ N₂—OH, —NHR or—NR₂; Y₂ represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or—OH; X₁ represents any one of a single bond, —CO—O—, —O—CO—, —COCH₂—,—CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one ofa single bond, —CO—O—, —O—CO—, —COCH₂ —, —CH₂—CO—, —CH₂O—, —OCH₂—,—CH₂—CH₂— or —CH═—CH—; A₁ represents any one of a single bond, aphenylene group or a cyclohexylene group; A₂ represents any one of asingle bond, a phenylene group or a cyclohexylene group; R₁ representsany one of an alkyl group or an alkoxy group; and R₂ represents any oneof an alkyl group or an alkoxy group.

[0063] The content of the dopant in the liquid crystal is generally 100ppm (1×10⁻⁴% by weight) or more, and preferably 1,000 ppm or more. Whena non-liquid crystal substance is incorporated in a liquid crystal, thecharacteristics of the liquid crystal (liquid crystal property) isdeteriorated, and when a too large amount of the non-liquid crystalsubstance is incorporated, such a temperature range in that the liquidcrystal behaves as a liquid crystal nature becomes narrow. In theinvention, since the dopant is incorporated in the liquid crystal in anamount of 100 ppm or more, preferably 1,000 ppm or more, the after imagecan be suppressed while decrease of the liquid crystal property of theliquid crystal is suppressed to the allowable range to constitute anactive matrix liquid crystal display device, whereby a liquid crystaldisplay device having excellent liquid crystal characteristics and lessafter image can be provided.

[0064] When the specific resistance of the liquid crystal is from1.0×10⁹ to 1.0×10¹² Ω·cm, a liquid crystal display device having lessafter image can be provided. When the liquid crystal has a specificresistance of more than 1.0×10¹² Ω·cm, the effect of suppressing theafter image cannot be conspicuously obtained, and when the liquidcrystal has a specific resistance of less than 1.0×10⁹ Ω·cm, highdisplay quality cannot be maintained.

[0065] The orientation film as the liquid crystal orientationcontrolling layer is formed to have a film thickness of from 20 nm to300 nm. When the film thickness of the orientation film is less than 20nm, the uniformity of the orientation film is deteriorated since theunevenness of the surface of the ITO film or the IZO film, which isformed under the orientation film, is from 10 nm to 20 nm, so as tocause display unevenness and to cause printing unevenness of theorientation film upon forming the orientation film. When the filmthickness of the orientation film is more than 300 nm, the orientationfilm is ununiformly dried, which causes display unevenness.

[0066] The insulating film is formed to have a film thickness of from0.1 μm to 4 μm. When the film thickness of the insulating film is lessthan 0.1 μm, the insulating property of the film is deteriorated, andwhen it exceeds 4 μm, the after image becomes conspicuous.

[0067] As the liquid crystal having negative dielectric anisotropy, aliquid crystal containing a liquid crystal molecule having adifluorinated benzene structure in the molecule and a liquid crystalcontaining a liquid crystal molecule having a dicyanobenzene structurein the molecule can be used.

[0068] Furthermore, a liquid crystal containing both a liquid crystalmolecule having a difluorinated benzene structure in the molecule and aliquid crystal molecule having a dicyanobenzene structure in themolecule can also be used. A liquid crystal containing a liquid crystalmolecule having a monocyanocyclohexane structure in the molecule canalso be used as the liquid crystal having negative dielectricanisotropy.

[0069] A liquid crystal containing both a liquid crystal molecule havinga difluorinated benzene structure in the molecule and a liquid crystalmolecule having a monocyanocyclohexane structure in the molecule canalso be used.

[0070] Moreover, in the case of a liquid crystal having positivedielectric anisotropy is used, the dissociative dopant can be added, andthe structures of the pixel electrode and the counter electrode arenormalized, whereby the occurrence of the after image can be suppressed.

[0071] One means is an active matrix liquid crystal display devicecomprising a pair of substrates; a liquid crystal layer sandwiched bysaid pair of substrates; orientation films defining an orientationdirection of a liquid crystal molecule of said liquid crystal layer,said orientation films being arranged between said pair of substratesand said liquid crystal layer; and a pixel electrode and a counterelectrode applying a voltage to said liquid crystal layer, said liquidcrystal molecule of said liquid crystal layer having positive dielectricanisotropy, and said liquid crystal layer containing a dopant having adissociative group.

[0072] A means with a liquid crystal composition comprising from 100 ppmto 1,000 ppm of a dopant having a dissociative group only in a shorteraxis direction of a molecule and having an alkyl group or an alkoxygroup on both ends of said shorter axis direction of a molecule iseffective.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073]FIG. 1 is a plane view showing a constitutional example of onepixel and a periphery thereof of a liquid crystal display part of anactive matrix color liquid display device.

[0074]FIG. 2 is a cross sectional view on line II-II in FIG. 1.

[0075]FIG. 3 is a cross sectional view of a thin film transistor (TFT)on line III-III in FIG. 1.

[0076]FIG. 4 is a cross sectional view of a storage capacitance (Cstg)forming part on line IV-IV in FIG. 1.

[0077]FIG. 5 is a diagram showing the relationship of an electric fieldapplication direction and a rubbing direction to a transmitting axis ofa polarizing plate.

[0078]FIG. 6 is a plane view showing a structure of a matrix peripheryof a display panel.

[0079]FIG. 7A is a diagram showing a panel edge part having a gatesignal terminal, and FIG. 7B is a diagram showing a panel edge parthaving no terminal for external connection.

[0080]FIGS. 8A and 8B are a plane view and a cross sectional view,respectively, of an example of a structure in the vicinity of aconnecting part of a gate terminal GTM and a gate line GL.

[0081]FIGS. 9A and 9B are a plane view and a cross sectional view,respectively, of an example of a structure in the vicinity of aconnecting part of a drain terminal DTM and a drain signal line DL.

[0082]FIGS. 10A and 10B are a plane view and a cross sectional view,respectively, of an example of a structure in the vicinity of aconnecting part of a counter electrode terminal CTM and a common basline CB with a common voltage signal line CL.

[0083]FIG. 11 is a diagram showing a circuit diagram of a matrix partand a periphery thereof of an active matrix color liquid crystal displaydevice.

[0084]FIG. 12 is a diagram showing a driving waveform of an activematrix color display device according to the invention.

[0085]FIG. 13 is a top view showing a liquid crystal display panelhaving a peripheral driving circuit mounted thereon.

[0086]FIGS. 14A to 14C are diagrams showing a production process of asubstrate SUB1.

[0087]FIGS. 15D to 15F are diagrams showing a production process of asubstrate SUB1 subsequent FIGS. 14A to 14C.

[0088]FIG. 16 is a plane view showing one pixel of another example of aliquid crystal display part of an active matrix color liquid crystaldisplay device.

[0089]FIGS. 17A and 17B are plane views showing one pixel of furtherexamples of a liquid crystal display part of an active matrix colorliquid crystal display device.

[0090]FIGS. 18A and 18B are plane views showing one pixel of furtherexamples of a liquid crystal display part of an active matrix colorliquid crystal display device.

[0091]FIGS. 19A and 19B are plane views showing one pixel of furtherexamples of a liquid crystal display part of an active matrix colorliquid crystal display device.

[0092]FIG. 20 is a cross sectional view showing one pixel of a furtherexample of a liquid crystal display part of an active matrix colorliquid crystal display device.

[0093]FIG. 21 is a cross sectional view showing one pixel of a furtherexample of a liquid crystal display part of an active matrix colorliquid crystal display device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0094] Embodiments of the invention will be described below withreference to the drawings. An example of an active matrix color liquidcrystal display device, to which the invention is applied, will bedescribed. In the drawings, the same symbols are attached to the partshaving the same functions to omit the repetition of explanation.

EXAMPLE 1

[0095] Plane Structure of Matrix Part (Pixel Part)

[0096]FIG. 1 is a plane view showing one pixel and a periphery thereofof an active matrix color liquid display device according to theinvention. The following description refers to a so-called thin filmtransistor liquid crystal display device using a thin film transistor(TFT) as an active matrix element.

[0097] As shown in FIG. 1, the pixel is arranged in the regionsurrounded by a gate signal line (a scanning signal line or a horizontalsignal line) GL, a common voltage signal line (a counter electrode line)CL and adjacent two drain signal lines (image signal lines or verticalsignal lines) DL crossing each other.

[0098] These signal lines each is formed with an opaque metallicelectrode. The gate signal line GL and the common voltage signal line CLare lied horizontally in FIG. 1, and pluralities thereof are arrangedvertically. The image signal line DL is laid vertically, and a pluralitythereof is arranged horizontally.

[0099] The pixel electrode PX is formed with an ITO transparentelectroconductive film and is electrically connected with (a sourceelectrode SD1 of) the thin film transistor TFT via a through hole. Thecounter electrode CT is also formed with ITO and is electricallyconnected with the common voltage signal line CL. The symbol SD2 denotesa drain electrode and AS denotes a semiconductor layer.

[0100] The pixel electrode PX is formed to has a comb form, each ofwhich is a long electrode extending in the vertical direction in FIG. 1.The counter electrode CT is a solid transparent electrode, and theoptical state of a liquid crystal composition LC is controlled by anelectric field generated between the pixel electrode PX and the counterelectrode CT.

[0101] The gate signal line GL is to transmit the gate signal to thethin film transistor TFT of the respective pixels, and the drain signalline DL is to supply the drain signal voltage to the pixel electrode PXof the respective pixels via (a drain electrode SD2 of) the thin filmtransistor TFT. The common voltage signal line CL is to supply thecommon voltage to the counter electrode CT of the respective pixels.

[0102] The common voltage signal line CL formed with a metallicelectrode is formed to surround the sides of the drain signal line DL,and it also functions as a light shielding layer for preventingunnecessary light leakage on the sides of the drain line caused byinfluence of an electric field formed by the potential of the drainelectrode.

[0103] The electrode width W and the electrode interval L of the pixelelectrode PX of a comb form are changed depending on the liquid crystalmaterial used. This is because since the intensity of the electric fieldthat attains the maximum transmissibility varies depending on the liquidcrystal material, the electrode interval is set depending on the liquidcrystal material, so as to obtain the maximum transmissibility withinthe range of the maximum amplitude of the signal voltage determined bythe withstanding voltage of the drain signal driving circuit (signaldriver) used.

[0104] The width of the pixel electrode is set at a range of from 1 μmto 15 μm, and in this example, it is set at 4 μm taking the openingratio and the productivity of the electrode into consideration. Theelectrode interval L is set at a range of from 1 μm to 10 μm, and inthis example, it is set at 4 μm for realizing the driving voltage of 10V or less.

[0105] Cross Sectional Structure of Matrix Part (Pixel Part)

[0106]FIG. 2 is a cross sectional view on line II-II in FIG. 1, FIG. 3is a cross sectional view of the thin film transistor TFT on lineIII-III in FIG. 1, and FIG. 4 is a cross sectional view of a storagecapacitance (Cstg) forming part on line IV-IV in FIG. 1.

[0107] As shown in FIGS. 2 to 4, on a lower transparent glass substrateSUB1 arranged under the liquid crystal composition layer (hereinaftersometimes simply referred to as a liquid crystal) LC, the thin filmtransistor TFT, the storage capacitance Cstg and the electrode group areformed, and on a upper transparent glass electrode SUB2, a color filterFIL and a light shielding black matrix pattern BM are formed.

[0108] Orientation films OR11 and OR12, which are liquid crystalorientation controlling layers for controlling the initial orientationof the liquid crystal, are formed on the inner surfaces (on the side ofthe liquid crystal LC) of the transparent glass substrates SUB1 andSUB2. Polarizing plates POL1 and POL2 are provided on the outer surfacesof the transparent glass substrates SUB1 and SUB2.

[0109] This example has such a structure as shown in FIGS. 2 to 4 thatthe counter electrode CT as solid ITO and the gate signal line GL are inthe same layer, and the pixel electrode PX as comb form ITO is formed ona protective insulating film PSV formed on the signal line DL.

[0110] Therefore, in the cross sectional view, the pixel electrode PXand the counter electrode CT are sandwiched by a gate insulating film GIand the protective insulating film PSV, which form the storagecapacitance Cstg.

[0111] The common signal line CL is in contact with the counterelectrode CT in the same layer. The gate insulating film GI and theprotective insulating film PSV may be formed with SiO₂ or Si_(x)N_(y).

[0112] In addition to the structure of the pixel electrode and thecounter electrode shown in FIG. 2, the following structures may beemployed. As shown in FIG. 20, a pixel electrode PX is formed with solidITO, and a counter electrode CT having a comb electrode part is arrangedabove the pixel electrode PX through a protective insulating film PSV2.As shown in FIG. 21, a pixel electrode is formed with solid ITO, and acounter electrode CT having a comb electrode part is arranged above thepixel electrode PX through a protective insulating film PSV1.

[0113] TFT Substrate

[0114] The structure of the lower transparent glass substrate SUB1 (aTFT substrate) will be described in detail below.

[0115] Thin Film Transistor TFT

[0116]FIG. 3 shows a cross sectional view of the part of the thin filmtransistor. The thin film transistor TFT function in such a manner thatwhen a positive bias is applied to agate electrode GT, the channelresistance between the source and the drain is decreased, and when thebias is zero, the channel resistance is increased.

[0117] The thin film transistor TFT has a gate electrode GT, a gateinsulating film GI, an i type (intrinsic, i.e., doped with no impuritydetermining the conductive type) semiconductor layer AS comprising itype amorphous silicon (Si), and a pair of electrodes (a sourceelectrode SD1 and a drain electrode SD2).

[0118] The source electrode SD1 and the drain electrode SD2 arefundamentally determined by the bias polarity between them, and thepolarity is repeatedly inverted during operation of the circuit of theliquid crystal display device. Therefore, it is understood that thesource electrode SD1 and the drain electrode SD2 are interchanged byeach other during operation. However, in the following description, oneof them is referred to as a source electrode and the other is referredto as a drain electrode for convenience.

[0119] Gate Electrode GT

[0120] The gate electrode GT is formed continuously from the gate signalline GL, and a part of the region of the gate signal line GL is formedas the gate electrode GT. The gate electrode GT is a region beyond theactive region of the thin film transistor TFT.

[0121] In this example, the gate electrode GT is formed with a singlelayer electroconductive film g1. The electroconductive film g1 may be,for example, a chromium-molybdenum (Cr—Mo) alloy film formed bysputtering, but it is not limited thereto. The electroconductive filmmay have a two-layer structure of different metals.

[0122] Gate Signal Line GL

[0123] The gate signal line GL is formed with a single layerelectroconductive film g1. The electroconductive film g1 of the gatesignal line GL is formed in the same production process as theelectroconductive film g1 of the gate electrode GT and is integratedtherewith.

[0124] A gate voltage GV is supplied from an outer circuit to the gateelectrode GT via the gate signal line GL. In this example, achromium-molybdenum (Cr—Mo) alloy film formed by sputtering, forexample, is used as the electroconductive film g1.

[0125] The material of the gate signal line GL and the gate electrode GTis not limited to a chromium-molybdenum alloy and may be, for example, atwo-layer structure comprising aluminum or an aluminum alloy wrappedwith a chromium-molybdenum alloy for decreasing the resistance.

[0126] Common Voltage Signal Line CL

[0127] The common voltage signal line CL is formed with anelectroconductive film g1. The electroconductive film g1 of the commonvoltage signal line CL is formed in the same production process as theelectroconductive film of the gate signal line GL and the gate electrodeGT and is integrated with the counter electrode CT.

[0128] A common voltage Vcom is supplied from an outer circuit to thecounter electrode CT via the common voltage signal line CL.

[0129] The material of the common voltage signal line CL is not limitedto a chromium-molybdenum alloy and may be, for example, a two-layerstructure comprising aluminum or an aluminum alloy wrapped with achromium-molybdenum alloy for decreasing the resistance.

[0130] Insulating Film GI

[0131] The insulating film GI is used as a gate insulating film forapplying an electric field to the semiconductor layer AS associated withthe gate electrode GT in the thin film transistor TFT. The insulatingfilm GI is formed as an upper layer of the gate electrode GT and thegate signal line GL.

[0132] As the insulating film GI, for example, a silicon nitride filmformed by plasma CVD is selected, which is formed to have a thickness offrom 100 nm to 4 μm (about 350 nm in this example).

[0133] The gate insulating film GI also functions as an interleveldielectric film of the gate signal line GL and the common voltage signalline CL with the drain signal line DL, and contributes to electricinsulation thereof.

[0134] i Type Semiconductor Layer AS

[0135] The i type semiconductor layer AS formed with an amorphoussilicon semiconductor at a thickness of from 15 nm to 250 nm (about 120nm in this example). A layer d0 is an N(+) type amorphous siliconsemiconductor layer doped with phosphorous (P) for ohmic contact, whichis left at a part, where the i type semiconductor layer AS is presentunder the layer d0, and an electroconductive layer d1 is present abovethe layer d0.

[0136] The i type semiconductor layer AS and the layer d0 are alsoprovided at a crossing part (a crossover part) of the gate signal lineGL and the common voltage signal line CL with the drain signal line DL.The i type semiconductive layer AS at the crossing part decreases theshort circuit of the gate signal line GL and the common voltage signalline CL with the drain signal line DL.

[0137] Source Electrode SD1 and Drain Electrode SD2

[0138] The source electrode SD1 and the drain electrode SD2 each isformed with the electroconductive layer d1 in contact with the N(+) typesemiconductive layer d0. A Cr—Mo film has low stress and thus can beformed to have a relatively large film thickness to contribute todecrease of the resistance of the line. The Cr—Mo film has good adhesionproperty to the N(+) type semiconductor layer d0.

[0139] Drain Signal Line DL

[0140] The drain signal line DL is formed in the same layer as thesource electrode SD1 and the drain electrode SD2. The drain signal lineDL is formed as integrated with the drain electrode SD2.

[0141] In this example, the electroconductive film d1 is achromium-molybdenum alloy (Cr—Mo) film formed by sputtering at athickness of from 50 nm to 300 nm (about 250 nm in this example). TheCr—Mo film has low stress and thus can be formed to have a relativelylarge film thickness to contribute to decrease of the resistance of theline.

[0142] The Cr—Mo film has good adhesion property to the N(+) typesemiconductor layer d0. As the electroconductive film d1, other than theCr—Mo film, a high melting point metal (such as Mo, Ti, Ta and W) filmand a high melting point metal silicide (such as MoSi₂, TiSi₂, TaSi₂ andWSi₂) film may also be used, and an accumulated layer structure withaluminum may also be used.

[0143] Storage Capacitance Cstg

[0144] An electroconductive film ITO2 forming the storage capacitanceCstg is formed to overlap an electroconductive film ITO1 forming thecounter electrode CT. The overlap constitutes a storage capacitance(electrical capacitance element) Cstg between the pixel electrode PX andthe counter electrode CT as understood from FIG. 2.

[0145] The dielectric film of the storage capacitance Cstg is formedwith the protective film PSV and the insulating film GI used as the gateinsulating film of the thin film transistor TFT. As shown in FIG. 4,from a plane view, the storage capacitance Cstg is formed as anoverlapping part of the pixel electrode PX and the counter electrode CTinside the pixel.

[0146] Protective Film PSV

[0147] The protective film PSV is formed on the thin film transistorTFT. The protective film PSV is provided mainly for protecting the thinfilm transistor from moisture, and a film having high transparency andhigh moisture resistance is used.

[0148] The protective film PSV is formed, for example, with a siliconoxide film or a silicon nitride film formed by using a plasma CVDapparatus at a film thickness of from 0.1 μm to 1 μm. The protectivefilm PSV is removed to expose outer connecting terminals DTM and GTM.

[0149] With respect to the thickness of the protective film PSV and theinsulating film GI, the thickness of the protective film PSV is madelarge taking the protection effect into consideration, and the thicknessof the insulating film GI is made thin taking the mutual conductance gmof the transistor into consideration. The protective film PSV may havean accumulated structure of an organic film, such as polyimide, having arelatively large thickness of from 2 μm to 3 μm.

[0150] Pixel Electrode PX

[0151] The pixel electrode PX is formed with ITO as a transparentelectroconductive material, and forms a storage capacitance with thecounter electrode CT, which is similarly formed with ITO. In thisexample, explanation is made by using ITO as the transparentelectroconductive material, but the same effect can be obtained by usingindium-zinc oxide (IZO).

[0152] Counter Electrode CT

[0153] The counter electrode CT is formed with ITO and is connected tothe common voltage signal line CL in the same layer. It is constitutedin such a manner that the common voltage Vcom is applied to the counterelectrode CT.

[0154] In this example, the common voltage Vcom is set at a potentialthat is lower than the intermediate direct current potential between theminimum level driving voltage Vdmin and the maximum level drivingvoltage Vdmax applied to the drain signal line DL by the feed throughvoltage ΔVs formed upon turning off the thin film transistor TFT.

[0155] In this example, explanation is made by using ITO as thetransparent electroconductive material, but the same effect can beobtained by using IZO.

[0156] Color Filter Substrate

[0157] The upper transparent glass substrate SUB2 (color filtersubstrate) will be described in detail with reference to FIGS. 1 and 2.

[0158] Light Shielding Film BM

[0159] On the upper transparent glass substrate SUB2, as a BM boundaryline shown by a heavy line in FIG. 1, a light shielding film BM (aso-called black matrix) is formed to prevent decrease of contrast causedby emission of transmitted light from an unnecessary gap (a gap otherthan that between the pixel electrode PX and the counter electrode CT)to the display surface.

[0160] The light shielding film BM also functions to prevent emission ofouter light or back light incident on the i type semiconductor layer AS.That is, the i type semiconductor layer As of the thin film transistorTFT is vertically sandwiched by the light shielding film BM and therelatively large gate electrode GT (FIG. 3) so as to prevent fromirradiation with outer natural light and back light.

[0161] Although the light shielding film BM in FIG. 1 is shown for onlyone pixel, it is formed to have openings inside the respective pixels.The pattern thereof used herein is a mere example.

[0162] At a part where the direction of the electric field is disturbed,such as an edge of the comb electrode, the display has one-to-onecorrespondence to the image information inside the pixel, and becomesblack in case of black or white in case of white. Therefore, it can beused as a part of display.

[0163] However, the light shielding film BM necessarily has a shieldingfunction to light. In particular, at the gap between the pixel electrodePX and the counter electrode CT, the optical density thereof isnecessarily 3 or more for preventing cross talk in the drain signal linedirection (vertical smear).

[0164] While the light shielding film BM may be formed with a metalhaving electroconductivity, such as Cr, it is preferably formed with afilm having high insulation property to prevent influence on theelectric field between the pixel electrode PX and the counter electrodeCT.

[0165] In this example, a black organic pigment is mixed with a resistmaterial and formed to a thickness of about 1.2 μm. In order to improvethe shielding property to light, carbon and titanium oxide (Ti_(x)O_(y))may be mixed in an amount of such a range that can maintain theinsulating property of 10⁸ Ω·cm or more, which does not affect theelectric field inside the liquid crystal composition layer.

[0166] Since the light shielding film BM comparts the effective displayregions of the respective lines, it also has a function of clarifyingthe contour of the pixel of the respective lines. The light shieldingfilm BM is also formed in the form of frame on the periphery, thepattern of which is formed continuously from the pattern of the matrixpart shown in FIG. 1.

[0167] The light shielding film BM in the periphery is extended beyond aseal part SL (see FIG. 7), so as to prevent invasion of leaked light,such as reflected light, caused by practical implementation, such as apersonal computer, to the matrix part, and also to prevent leakage oflight, such as back light, to the outside of the display area.

[0168] The light shielding film BM is terminated inside the edge of thesubstrate SUB2 by about 0.3 mm to 1.0 mm, so as to form around the cutregion of the substrate SUB2.

[0169] Color Filter FIL

[0170] The color filter FIL is formed in a stripe form comprisingrepeating colors, red, green and blue, at the counter position of thepixels. The color filter FIL is formed to overlap the light shieldingfilm BM.

[0171] The color filter FIL can be formed in the following manner. Adyeing base material, such as an acrylic resin, is formed on the surfaceof the upper transparent glass substrate SUB2, and the dyeing basematerial on the region other than the red filter forming region isremoved by the photolithography technique.

[0172] Thereafter, the remaining dyeing base material is dyed with a redpigment, followed by subjecting to a fixing treatment, so as to form ared filter R. A green filter G and a blue filter B are then formed inthe same manner. The dyeing can also be conducted with a dye.

[0173] Overcoating Film OC

[0174] An overcoating film OC is provided for preventing leakage of thedyes of the color filter FIL to the liquid crystal composition layer LCand for flattening steps formed by the color filter FIL and the lightshielding film BM.

[0175] The overcoating layer is formed, for example, with a transparentresin material, such as an acrylic resin and an epoxy resin. An organicfilm, such as polyimide having good flowability, can also be used as theovercoating layer.

[0176] Liquid Crystal Layer and Polarizing Plate

[0177] The liquid crystal layer, the orientation film and the polarizingplate will be described below.

[0178] Liquid Crystal Layer

[0179] In this example, a nematic liquid crystal having a negativedielectric anisotropy Δ∈ of a value of 4.0 and a refractive indexanisotropy Δn of 0.100 (589 nm, 20° C.) containing a liquid crystalmolecule having a difluorinated benzene structure in the molecule isused as the liquid crystal.

[0180] In addition to the above, a liquid crystal having a dielectricanisotropy Δ∈, a liquid crystal containing a liquid crystal moleculehaving a dicyanobenzene structure in the molecule, a liquid crystalcontaining a liquid crystal molecule having a difluorinated benzenestructure in the molecule, a liquid crystal containing a liquid crystalmolecule having a dicyanobenzene structure in the molecule, a liquidcrystal containing a liquid crystal molecule having amonocyanocyclohexane structure in the molecule and a liquid crystalcontaining both a liquid crystal molecule having a difluorinated benzenestructure in the molecule and a liquid crystal molecule having amonocyanocyclohexane structure in the molecule can be used. The liquidcrystal is not limited to the foregoing composition and may be used asfar as it is a liquid crystal having negative dielectric anisotropy.

[0181] The thickness of the liquid crystal composition layer (gap) is3.0 μm, and the retardation is 0.30 μm. It is combined with theorientation film and the polarizing plate described later in such amanner that the maximum transmittance can be obtained when the liquidcrystal molecules are rotated from the initial orientation direction toabout 45° in the direction of the electric field, and transmitted lighthaving substantially no dependency on the wavelength within the range ofvisible light can be obtained.

[0182] The thickness of the liquid crystal composition layer (gap) iscontrolled with polymer beads having been subjected to a verticalorientation treatment, whereby the orientation of the liquid crystalmolecules in the vicinity of the beads upon displaying black isstabilized to obtain a good black level, so as to improve the contrastratio.

[0183] The specific resistance of the liquid crystal is from 1.0×10¹⁰ to1.0×10¹² Ω·cm (5.2×10¹¹ Ω·cm in this example). According to the system,the voltage charged between the pixel electrode and the counterelectrode can be sufficiently maintained even when the resistance of theliquid crystal is low.

[0184] The lower limit thereof is 1.0×10⁹ Ω·cm, and preferably 1.0×10¹⁰Ω·cm. This is because the pixel electrode and the counter electrode areconstituted on the same substrate. When the resistance is too high,static charge formed during the production process is difficult to berelaxed, and therefor it is 1.0×10¹³ Ω·cm or less, and preferably1.0×10¹² Ω·cm or less.

[0185] Orientation Film

[0186] Polyimide is used as the orientation film ORI. The initialorientation directions RDR of the upper and the lower substrates areparallel to each other. As a method for applying the initial orientationdirection, rubbing is generally employed, and oblique vapor depositionmay also be used.

[0187] The relationship between the initial orientation direction RDRand the applied electric field direction EDR is shown in FIG. 5. In thisexample, the initial orientation direction RDR is about 75° with respectto the horizontal direction. In the constitution of this example usingthe liquid crystal composition having negative dielectric anisotropy,the angle formed between the initial orientation direction RDR and theapplied electric field direction EDR is necessarily 45° or more and lessthan 90°. The orientation film is formed to have a thickness of from 20nm to 300 nm (about 100 nm in this example).

[0188] Polarizing Plate

[0189] A polarizing plate having electroconductivity is used as thepolarizing plates POL1 and POL2. The polarized light transmitting axisMAX1 of the upper polarizing plate POL1 agrees to the initialorientation direction RDR, and the polarized light transmitting axisMAX2 of the lower polarizing plate POL2 is perpendicular thereto. Therelationships are shown in FIG. 5.

[0190] According to the configuration, normally close characteristicscan be obtained in that the transmittance is increased associated withincrease of the voltage applied to the pixel of the invention (thevoltage between the pixel electrode PX and the counter electrode CT).When no voltage is applied, black display of good quality can beobtained.

[0191] In this example, countermeasures for display failure caused byexternal static charge and EMI are conducted by impartingelectroconductivity to the polarizing plates. The electroconductivity ispreferably a sheet resistance of 10⁸Ω per square or less when thecountermeasure only for static charge is necessary, and is preferably asheet resistance of 10⁴Ω per square or less when the countermeasure forEMI is also necessary. It is also possible to provide anelectroconductive layer on the surface of the glass substrate oppositeto the surface having the liquid crystal composition supported thereon(i.e., the surface having the polarizing plate is adhered).

[0192] Constitution Around Matrix

[0193]FIG. 6 is a plane view showing an important part around a matrix(AR) of the display panel PNL containing the upper and lower glasssubstrates SUB1 and SUB2. FIG. 7A is a cross sectional view showing thepart around the external connecting terminal GTM, to which a scanningcircuit is to be connected, and FIG. 7B is a cross sectional viewshowing the part around the seal part having no external connectingterminal.

[0194] Upon production of the panel, plural devices are worked on oneglass substrate, followed by dividing, to improve the throughput whenthe size is small, and when the size is large, in order for common useof the production equipments, a glass substrate of the standardized sizeis worked for any kind of product, followed by cutting into the size forthe respective kinds of product.

[0195] In any case, the glass is cut after subjecting the predeterminedprocess. FIGS. 6, 7A and 7B show the latter example and shows the stateafter cutting the upper and lower substrates SUB1 and SUB2. The symbolLN in FIG. 6 means the edges of the substrates before cutting.

[0196] In any case, the size of the upper substrate SUB2 is limitedinside the lower substrate SUB1 in the finalized state in such a mannerthat the part having the external connecting terminals Tg and Td and theterminal CTM (the upper periphery and the left periphery in FIG. 6) isexposed.

[0197] The terminals Tg and Td refer to a plurality of units of tapecarrier packages TCP (see FIG. 13) containing a scanning circuitconnecting terminal GTM and a drain signal circuit connecting terminalDTM, both of which will be described later, as well as outgoing lineparts thereof mounted on an integrated circuit chip CHI (see FIG. 13).

[0198] The groups of the outgoing lines from the matrix part to theexternal connecting terminal part is inclined toward the both endsthereof. This is because the terminals DTM and GTM of the display panelPNL are conformed to the intervals of the arrangement of the package TCPand the connecting terminals of the package TCP.

[0199] The counter electrode terminal CTM is a terminal for applying thecommon voltage from an external circuit to the counter electrode CT. Thecommon voltage signal line CL in the matrix part is drawn to theopposite side of the scanning circuit terminal GTM (the right side inFIG. 6), and the respective common voltage signal lines are integratedto a common bas line CB, which is connected to the counter electrodeterminal CTM.

[0200] A seal pattern SL is formed along the edges of the transparentglass substrates SUB1 and SUB2 to seal the liquid crystal CL except fora liquid crystal inlet INJ. The sealing material comprises, for example,an epoxy resin. The layers of the orientation films ORI1 and ORI2 areformed inside the seal pattern SL. The polarizing plates POL1 and POL2are formed on the outer surfaces of the lower transparent glasssubstrate SUB1 and the upper transparent glass substrate SUB2,respectively. The liquid crystal LC is filled in the region comparted bythe seal pattern SL between the lower orientation film ORI1 and theupper orientation film ORI2 setting the direction of the liquid crystalmolecules. The lower orientation film ORI1 is formed above theprotective film PSV on the side of the lower transparent glass substrateSUB1.

[0201] The liquid crystal display device is fabricated in such a mannerthat the various layers are accumulated separately on the side of thelower transparent glass substrate SUB1 and the side of the uppertransparent glass substrate USB2, and the lower transparent glasssubstrate SUB1 and the upper transparent glass substrate SUB2 aresuperimposed each other. Thereafter, the liquid crystal LC is filledfrom the opening INJ of the seal material SL, and the injection openingINJ is sealed, for example, with an epoxy resin, followed by cutting theupper and lower substrates.

[0202] Gate Terminal Part

[0203]FIGS. 8A and 8B are diagrams showing the connecting structure fromthe gate signal line of the display matrix to the external connectionterminal GTM thereof. FIG. 8A is a plane view, and FIG. 8B is a crosssectional view on line B-B in FIG. 8A.

[0204]FIGS. 8A and 8B correspond to the left lower part of FIG. 6, andthe part of the inclined line is expressed by a straight line forconvenience. In FIGS. 8A and 8B, hatching is given to the Cr—Mo layer g1for easy understanding.

[0205] The gate terminal GTM comprises the Cr—Mo layer g1 and atransparent electroconductive layer ITO1 for protecting the surface ofthe Cr—Mo layer and for improving the reliability of the connection tothe TCP (tape carrier package).

[0206] The transparent electroconductive layer ITO1 is formed with atransparent electroconductive film ITO. As shown in FIG. 8B, theinsulating film GI and the protective film PSV are formed on the rightside of FIG. 8B, and the terminal part GTM on the left edge is exposedfrom the insulating film GI and the protective film PSV to enableelectric contact with an outer circuit.

[0207] While only one pair of the gate line GL and the gate terminal GTMis shown in FIGS. 8A and 8B, plurality of the pairs are actuallyarranged in the vertical direction to constitute a group of theterminals Tg (see FIG. 10), and the left side in FIGS. 8A and 8B of thegate terminal GTM is extended beyond the cutting region of thesubstrates during the production process and is shorted with a shortcircuit line SHg (not shown in the figure). The short circuit formed bythe short circuit line SHg prevents electrostatic damage of theorientation film ORI1 due to rubbing during the production process.

[0208] Drain Terminal DTM

[0209]FIGS. 9A and 9B are diagrams showing the connecting structure fromthe drain signal line DL to the external connecting terminal DTMthereof. FIG. 9A is a plane view, and FIG. 9B is a cross sectional viewon line B-B in FIG. 9A. FIGS. 9A and 9B correspond to the right upperpart of FIG. 6, and the right end corresponds to the upper end of thesubstrate SUB1 while the aspect of the figures is changed forconvenience.

[0210] The external connecting drain terminal DTM is arranged in thevertical direction, and the drain terminal DTM constitutes the group ofterminals Td (suffix omitted) as shown in FIG. 13 and are extendedbeyond the cutting line of the substrate SUB1. The drain terminal DTM isextended beyond the cutting region of the substrate during theproduction process, and all of them are shorted with a short circuitline SHd (not shown in the figure) for preventing electrostatic damage.

[0211] The drain connecting terminal DTM is formed with a transparentelectroconductive layer ITO1 and is connected to the drain signal lineDL at the part where the protective film PSV is removed. The transparentelectroconductive film ITO1 is formed with a transparentelectroconductive film ITO as similar to the case of the gate terminalGTM. The outgoing line from the matrix part to the drain terminal partDTM is formed with the layer d1, which is the same level as the drainsignal line DL.

[0212] Counter Electrode Terminal CTM

[0213]FIGS. 10A and 10B are diagrams showing the connecting structurefrom the common voltage signal line CL to the external connectingterminal CTM thereof. FIG. 10A is a plane view, and FIG. 10B is a crosssectional view on line B-B in FIG. 10A. FIGS. 10A and 10B correspond tothe left upper part of FIG. 6.

[0214] The respective common voltage signal lines CL are integrated to acommon bas line CB, which is withdrawn to the counter electrode terminalCTM. The common bas line CB has such a structure that anelectroconductive layer g3 (not shown in the figure) is accumulated onthe electroconductive layer g1, which are electrically connected withthe transparent electroconductive layer ITO1.

[0215] This is because the resistance of the common bas line CB isdecreased, and the common voltage is sufficiently supplied from anexternal circuit to the respective common voltage signal lines CL. Thestructure has such characteristics that the resistance of the common basline can be decreased without addition of another electroconductivelayer.

[0216] The counter electrode terminal has such a structure that thetransparent electroconductive layer ITO1 is accumulated on theelectroconductive layer g1. The transparent electroconductive film ITO1is formed with a transparent electroconductive film ITO as similar tothe cases of the other terminals.

[0217] The electroconductive layer g1 is covered with the transparentelectroconductive layer ITO1 to protect the surface thereof and toprevent electric corrosion thereof.

[0218] The connection of the transparent electroconductive layer ITO1with the electroconductive layer g1 and the electroconductive layer d1is effected through a through hole formed via the protective film PSVand the insulating film GI.

[0219] Total Equivalent Circuit of Display Device

[0220] A wiring diagram of the equivalent circuit of the display matrixpart and a peripheral circuit thereof is shown in FIG. 11. While FIG. 11is a circuit diagram, it is drawn to correspond to the actual geometricarrangement.

[0221] Plural pixels are two-dimensionally arranged to form a matrixarray. In FIG. 11, the symbol X denotes the drain signal line DL, andthe suffixes G, B and R are attached to correspond to a green pixel, ablue pixel and a red pixel, respectively. The symbol Y denotes a gatesignal line GL, and the suffixes 1, 2, 3 to end are attached tocorrespond to the order of scanning timing.

[0222] The gate signal line Y (suffix omitted) is connected to avertical scanning circuit V, and the drain signal line X (suffixomitted) is connected to a drain signal driving circuit H. The symbolSUP denotes a circuit containing a power source circuit for obtainingplural stabilized power sources obtained by dividing one power sourceand a circuit for converting display information from a host (hostoperation processing device) for a CRT (cathode ray tube) to displayinformation for a TFT liquid crystal display device.

[0223] Driving Method

[0224]FIG. 12 shows a driving waveform of the liquid crystal displaydevice of this example. A gate signal VG takes an on-level per onescanning period, and the others take an off-level. A drain signalvoltage VD is applied in such a manner that a positive pole and anegative pole are applied to one pixel by inverting per one flame at anamplitude of twice the voltage to be applied to the liquid crystallayer.

[0225] The polarity of the drain signal voltage VD is inverted per onecolumn and is also inverted per two lines. Accordingly, pixels havinginverted polarities are arranged adjacent to each other in the verticaland horizontal directions (i.e., dot inversion driving), and thusflicker and cross talk (smear) are difficult to be formed.

[0226] The common voltage Vc is set at a voltage below the centervoltage of the polarity inversion of the drain signal voltage by aconstant amount. This is to compensate the feedthrough voltage formedupon changing the thin film transistor TFT from the on-state to theoff-state, and is conducted by applying an alternating current voltageVLC having less direct current component to the liquid crystal. (Aliquid crystal suffers severe after image and deterioration when adirect current is applied thereto.)

[0227] Surface Panel PNL and Driving Circuit Board PCB1

[0228]FIG. 13 shows a top view showing the sate where the display panelPNL shown in FIG. 6 having the drain signal driving circuit H and thevertical scanning circuit V connected thereto.

[0229] The symbol CHI denotes a driving IC chips for driving the displaypanel PNL (in which the lower five chips are driving IC chips for thevertical scanning circuit, and the left ten chips are driving IC chipsfor the drain signal driving circuit).

[0230] The symbol TCP denotes a tape carrier package having the drivingIC chips CHI are mounted by a tape automated bonding method (TAB), andPCB1 denotes a driving circuit board having the TCP and capacitorsmounted thereon, which is divided into two, i.e., one for the drainsignal driving circuit and the other for the gate signal drivingcircuit.

[0231] The symbol FGP denotes a flame ground pad, which is soldered to aspring form fragment provided by cutting a shield case SHD. The symbolFC denotes a flat cable connecting the lower driving circuit board PCB1and the left driving circuit board PCB1.

[0232] As the flat cable FC, one comprising plural lead wires(comprising phosphor bronze plated with Sn) supported by sandwichingwith a polyethylene layer in a stripe form and a polyvinyl alcohol layeris used.

[0233] Production Process

[0234] The production process of the substrate SUB1 of the liquidcrystal display device described in the foregoing will be described withreference to FIGS. 14A to 14C and 15D to 15F below. In FIGS. 14A to 14Cand 15D to 15F, abbreviated names of the steps are shown in the centerof the figures, and the work flow is shown by cross sectional views, inwhich the thin film transistor TFT part shown in FIG. 3 is shown on theleft side, and the part around the gate terminal shown in FIGS. 8A and8B is shown on the left side.

[0235] The steps A to F are divided corresponding to the respectivephotographic processes, and the cross sectional views of the steps showthe stage where the treatment after the photographic process iscompleted, and the photoresist has been removed.

[0236] The photographic process referred herein means a series ofoperations including coating of a photoresist, selective exposurethrough a mask and development thereof. The steps A to C will bedescribed with reference to FIGS. 14A to 14C, and the steps D to F willbe described with reference to FIGS. 15D to 15F, but repetition ofexplanation will be omitted.

[0237] (a) Step A

[0238] An electroconductive film ITO1 comprising ITO having a filmthickness of 100 Å is provided on a lower transparent glass substrateSUB1 comprising AN635 Glass (a trade name) by sputtering. Aftersubjecting to a photographic process, the electroconductive film ITO1 isselectively etched with an HBr solution, so as to form a counterelectrode CT.

[0239] (b) Step B

[0240] An electroconductive film g1 comprising Cr having a filmthickness of 200 nm is provided by sputtering. After subjecting to aphotographic process, the electroconductive film g1 is selectivelyetched with ceric nitrate ammon, so as to form a gate electrode GT, agate signal line GL, a common voltage signal line CL, a gate terminalGTM, a first electroconductive layer of a common bas line CB, a firstelectroconductive layer of a counter electrode terminal CTM1 and a basline SHg (not shown in the figure) connecting the gate terminal GTM. Thematerial of the electrode is not limited to Cr, and Mo, Ti, Ta, W and analloy thereof may be used.

[0241] (c) Step C

[0242] An ammonia gas, a silane gas and a nitrogen gas are introducedinto a plasma CVD apparatus to provide a silicon nitride film having afilm thickness of 350 nm. A silane gas and a hydrogen gas are introducedinto the plasma CVD apparatus to provide an i type amorphous Si filmhaving a film thickness of 120 nm is provided, and then a hydrogen gasand a phosphine gas are introduced into the plasma CVD apparatus toprovide an N(+) type amorphous Si film having a film thickness of 30 nm.

[0243] After subjecting to a photographic process, the N(+) typeamorphous Si film and the i type amorphous Si film are selectivelyetched by using SF₆ and CCl₄ as a dry etching gas, so as to form islandsof an i type semiconductor layer AS.

[0244] (d) Step D

[0245] An electroconductive film d1 comprising Cr having a filmthickness of 30 nm is provided by sputtering. After subjecting to aphotographic process, the electroconductive film d1 is etched by thesame liquid as in the step B, so as to form a drain signal line DL, asource electrode SD1, a drain electrode SD2, a first electroconductivelayer of a common bas line CB2 and a bas line SHd (not shown in thefigure) shorting the drain terminal DTM. The material of the electrodeis not limited to Cr, and Mo, Ti, Ta, W and an alloy thereof may beused.

[0246] The N(+) type amorphous Si film is etched by introducing CCl₄ andSF₆ into a dry etching apparatus, so as to selectively remove the N(+)type semiconductor layer d0 between the source and the drain.

[0247] After patterning the electroconductive film d1 with a maskpattern, the N(+) type semiconductor layer d0 is removed by using theelectroconductive film d1 as a mask. That is, the N(+) typesemiconductor layer do remaining on the i type semiconductor layer AS isremoved in a self aligning manner except for the part where theelectroconductive film d1 is present. At this time, since the wholethickness of the N(+) type semiconductor layer d0 is removed by etching,the surface part of the i type semiconductor layer AS is also slightlyetched, and the extent thereof can be controlled by the etching time.

[0248] (e) Step E

[0249] An ammonia gas, a silane gas and a nitrogen gas are introducedinto the plasma CVD apparatus to provide a silicon nitride film having afilm thickness of 0.4 μm. After subjecting to a photographic process,the silicon nitride film is selectively etched by using SF₆ as a dryetching gas, so as to pattern a protective film PSV and an insulatingfilm GI.

[0250] (f) Step F

[0251] An electroconductive film ITO2 comprising ITO having a filmthickness of 12 nm is provided by sputtering. After subjecting to aphotographic process, the electroconductive film ITO2 is selectivelyetched with an HBr solution, so as to form a pixel electrode PX.

[0252] Dissociative Dopant

[0253] The characteristic feature of this example is that 100 ppm of2,5-dimethylphenol is added to the mother liquid crystal. The motherliquid crystal has a specific resistance of 1.9×10¹³ Ω·cm and an NIpoint of 70.5° C. When 2,5-dimethylphenol shown by the followingstructural formula is added thereto, the specific resistance becomes5.2×10¹¹ Ω·cm. The NI point of the liquid crystal is 70.4° C., which issubstantially the same as the liquid crystal before the addition.

[0254] The dissociative dopant used in this example means an acidicdissociative substance or a basic dissociative substance, or in otherwords, a substance generating an H+ ion through dissociation by itselfin a polar solvent or generating an OH⁻ ion through a reaction withwater.

[0255] Specific examples thereof include a carboxylic acid (including ananhydride thereof), an amide, an amine and an alcohol. When thesesubstances are added to a liquid crystal, the ion concentration in theliquid crystal is increased, so as to decrease the specific resistance.

[0256] Evaluation of display quality of the liquid crystal displaydevice of Example 1 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 2

[0257] Example 2 of a liquid crystal display device according to theinvention is the same as Example 1 except that the addition amount ofthe dopant used is changed to 1,000 ppm. The mother liquid crystal has aspecific resistance of 1.9×10¹³ Ω·cm and an NI point of 70.5° C. When2,5-dimethylphenol is added thereto, the specific resistance becomes2.5×10¹⁰ Ω·cm. The NI point of the liquid crystal is 70.2° C., which issubstantially the same as the liquid crystal before the addition.

[0258] Evaluation of display quality of the liquid crystal displaydevice of Example 2 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 3

[0259] Example 3 of a liquid crystal display device according to theinvention is the same as Example 1 except that the thickness of theorientation film used is changed to 50 nm.

[0260] Evaluation of display quality of the liquid crystal displaydevice of Example 3 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 4

[0261] Example 4 of a liquid crystal display device according to theinvention is the same as Example 1 except that the thickness of theorientation film used is changed to 300 nm.

[0262] Evaluation of display quality of the liquid crystal displaydevice of Example 4 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 5

[0263] Example 5 of a liquid crystal display device according to theinvention is the same as Example 1 except that the distance between thepixel electrodes is 2 μm.

[0264] Evaluation of display quality of the liquid crystal displaydevice of Example 5 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 6

[0265] Example 6 of a liquid crystal display device according to theinvention is the same as Example 1 except that a nematic liquid crystalcontaining a liquid crystal molecule having a monocyanocyclohexanestructure in the molecule is used. The mother liquid crystal has aspecific resistance of 3.5×10¹² Ω·cm and an NI point of 71.5° C. When2,5-dimethylphenol is added thereto, the specific resistance becomes2.5×10¹¹ Ω·cm. The NI point of the liquid crystal is 71.2° C., which issubstantially the same as the liquid crystal before the addition.

[0266] Evaluation of display quality of the liquid crystal displaydevice of Example 6 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 7

[0267] Example 7 of a liquid crystal display device according to theinvention is the same as Example 1 except that 500 ppm of2,5-dimethylaniline shown by the following structural formula is used asthe dopant. The mother liquid crystal has a specific resistance of1.9×10¹³ Ω·cm and an NI point of 70.5° C.

[0268] When 2,5-dimethylaniline is added thereto, the specificresistance becomes 1.2×10¹¹ Ω·cm. The NI point of the liquid crystal is70.1° C., which is substantially the same as the liquid crystal beforethe addition.

[0269] Evaluation of display quality of the liquid crystal displaydevice of Example 7 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 8

[0270] Example 8 of a liquid crystal display device according to theinvention is the same as Example 1 except that 2,000 ppm of2,5-dimethoxyphenol shown by the following structural formula is used asthe dopant. The mother liquid crystal has a specific resistance of1.9×10¹³ Ω·cm and an NI point of 70.5° C. When 2,5-dimethoxyphenol isadded thereto, the specific resistance becomes 1.2×10¹⁰ Ω·cm. The NIpoint of the liquid crystal is 70.3° C., which is substantially the sameas the liquid crystal before the addition.

[0271] Evaluation of display quality of the liquid crystal displaydevice of Example 8 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 9

[0272] Example 9 of a liquid crystal display device according to theinvention is the same as Example 1 except that 300 ppm of2,5-diethoxy-4-morphorinoaniline dihydrochloride shown by the followingstructural formula is used as the dopant. The mother liquid crystal hasa specific resistance of 1.9×10¹³ Ω·cm and an NI point of 70.5° C. When2,5-diethoxy-4-morphorinoaniline dihydrochloride is added thereto, thespecific resistance becomes 2.5×10¹¹ Ω·cm. The NI point of the liquidcrystal is 70.2° C., which is substantially the same as the liquidcrystal before the addition.

[0273] Evaluation of display quality of the liquid crystal displaydevice of Example 9 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

EXAMPLE 10

[0274] Example 10 of a liquid crystal display device according to theinvention is the same as Example 1 except that 900 ppm of4-(2,5-diethoxy-4-nitrophenyl)morphrinone shown by the followingstructural formula is used as the dopant. The mother liquid crystal hasa specific resistance of 1.9×10¹³ Ω·cm and an NI point of 70.5° C. When2,5-diethoxy-4-morphorinoaniline dihydrochloride is added thereto, thespecific resistance becomes 8.9×10¹⁰ Ω·cm. The NI point of the liquidcrystal is 70.2° C., which is substantially the same as the liquidcrystal before the addition.

[0275] Evaluation of display quality of the liquid crystal displaydevice of Example 10 according to the invention is conducted and revealsthat high quality display is confirmed, and substantially no formationof after image failure is observed.

Comparative Example 1

[0276] Comparative Example 1 of a liquid crystal display device is thesame as Example 1 except that2-cyano-3-fluoro-5-(4-n-propyl-trans-cyclohexyl)phenol shown by thefollowing structural formula is used as the dopant. The mother liquidcrystal has a specific resistance of 1.9×10¹³ Ω·cm and an NI point of70.5° C. When 1,000 ppm of2-cyano-3-fluoro-5-(4-n-propyl-trans-cyclohexyl)phenol is added thereto,the specific resistance becomes 3.3×10¹¹ Ω·cm. The NI point of theliquid crystal is 70.4° C., which is substantially the same as theliquid crystal before the addition.

[0277] Evaluation of display quality of the liquid crystal displaydevice of Comparative Example 1 i s conducted and reveals that highquality display is confirmed, but an after image failure is observed.

Comparative Example 2

[0278] Comparative Example 2 of a liquid crystal display device is thesame as Example 1 except that2-cyano-3-fluoro-5-(4-n-propyl-trans-bicyclohexyl)phenol shown by thefollowing structural formula is used as the dopant. The mother liquidcrystal has a specific resistance of 1.9×10¹³ Ω·cm and an NI point of70.5° C. When 100 ppm of2-cyano-3-fluoro-5-(4-n-propyl-trans-bicyclohexyl)phenol is addedthereto, the specific resistance becomes 5.5×10¹² cm. The NI point ofthe liquid crystal is 70.3° C., which is substantially the same as theliquid crystal before the addition.

[0279] Evaluation of display quality of the liquid crystal displaydevice of Comparative Example 2 is conducted and reveals that highquality display is confirmed, but an after image failure is observed.

[0280]FIG. 16 is a plane view of another example of the invention. Inthis example, a pixel electrode PX and counter electrodes CT1 and CT2are in a wave form (a zigzag form). According to the constitution, tworegions (domains) having reorientation states that are different fromeach other in direction are formed, and thus they compensates by eachother inversion of coloring and gradation in oblique directions, wherebya wide viewing angle can be obtained.

[0281] That is, the respective electrodes have a zigzag form havingplural crooked parts in the running direction thereof, and one side onthe crooked part has an angle θ with respect to the vertical directionRDRP in FIG. 16, whereas the other side on the crooked part has an angle180°-θ.

[0282] According to the configuration, the two regions (domains) havingreorientation states that are different from each other in direction areformed, and thus they compensates by each other inversion of coloringand gradation in oblique directions, whereby a wide viewing angle can beobtained.

[0283] The vertical direction RDRP also shows the initial orientationdirection of an orientation film ORI for a liquid crystal moleculehaving positive dielectric anisotropy (Np liquid crystal), and thehorizontal direction RDRN shows the initial orientation direction of anorientation film ORI for a liquid crystal molecule having negativedielectric anisotropy (Nn liquid crystal). In the pixel structure ofthis example, both the liquid crystal molecules having positivedielectric anisotropy and negative dielectric anisotropy.

[0284] In FIG. 16, a gate insulating film GI is formed between the pixelelectrode PX and the counter electrodes CT1 and CT2 as similar to theother examples, and an electric field in the horizontal directionrotating the liquid crystal molecule is formed between the electrodes.

[0285] A gate signal line GL and a drain signal line DL are the same asin the other examples. An amorphous semiconductor layer ASI is arrangedbetween an electrode SD2 formed from the drain signal line DL asoverlapping the gate signal line and an electrode SD1 connected to thepixel electrode for applying a storage voltage, so as to function as athin film transistor TFT.

[0286] A protective film PSV is formed on the thin film transistor TFT.The protective film PSV is provided mainly for protecting the thin filmtransistor from moisture, and a film having high transparency and highmoisture resistance is used.

[0287] The protective film PSV is formed, for example, with a siliconoxide film or a silicon nitride film formed by using a plasma CVDapparatus, or in alternative, with an acrylic resin or polyimide, tohave a film thickness of about from 0.1 μm to 3 μm.

[0288] A counter voltage signal line CL is formed by the same productionstep as the gate electrode, the scanning signal line GL and the counterelectrode CT, and is constituted as capable of electrically connectingwith the counter electrode CT. A counter voltage Vcom is supplied froman external circuit to the counter electrode CT via the counter voltagesignal line CL.

[0289] The part crossing the image signal line DL is narrowed todecrease the probability of shorting with the image signal line DL, andmay be formed in a bifurcated form, whereby they can be separated bylaser trimming even when they form a short circuit.

[0290] An electrode ST is formed with a metallic film (a layercontaining metallic atoms) and is connected to the pixel electrode PXvia a through hole TH1. Furthermore, it is necessary that a potential issupplied to the electrode ST from the outside, and a floating electrodeexhibits no effect. Therefore, it is connected to the other electrode byopening the through hole TH1 in the protective film PSV.

[0291] In this example, the electrode ST formed as integrated with thepixel electrode PX overlaps the counter electrode CT2 via the protectivefilm PSV.

[0292] In order to ensure the contact even when scattering occurs onproduction of the through hole and the electrode ST, the pixel electrodePX is provided on a base larger than the pixel electrode that isprovided at a part meeting the through hole TH1 at the end of the pixelelectrode to be integrated with the pixel electrode PX.

[0293] As described in the foregoing, in this example, the electrode STelectrically connected to the pixel electrode is formed on theprotective film PSV. According to the configuration, a capacitance (aprotective film capacitance), which is formed consequently between thepixel electrode PX and the counter electrodes CT1 and CT2 with theprotective film PSV or the protective film PSV and the insulating filmGI as a dielectric material, is charged through the electrode ST, andwhen an electrode having the same direct current potential (in the caseof alternating current, the potential of the direct current component)as the electrode ST is exposed to the liquid crystal layer due to aforeign matter, no charging current flows.

[0294] Therefore, no electrochemical reaction (electrode reaction)occurs in the vicinity of the exposed electrode. That is, since theelectrode ST is formed on the protective film PSV, the charging currentto the protective film capacitance of the other electrode due to adefect of the protective film on the electrode is suppressed, so as tosuppress formation of spot type brightness difference area.

[0295] Particularly, in the invention, the gate electrode GT or thescanning signal line is defined as an electrode or a line on the cathodeside. Furthermore, an electrode or a line having a higher potential thanthe gate electrode GT or the scanning signal line GL are defined as anelectrode or a line on the anode side, and the electrode or the line onthe anode side includes the source electrode SD1, the drain electrodeSD2, the image signal line DL, the pixel electrode PX, the counterelectrodes CT1 and CT2, and the counter voltage signal line CL.

[0296] As described in the foregoing, in the invention, while theelectrode ST is electrically connected to the pixel electrode as anexample of the electrode or the line on the anode side, the electrode STmay be connected to an electrode or a line comprising one or both thecathode and the anode.

[0297]FIGS. 17A, 17B, 18A, 18B, 19A and 19B are plane views showingmodified examples of the pixel described in FIG. 16. In FIGS. 17A, 17B,18A, 18B, 19A and 19B, the pixel electrode PX and the counter electrodeCT each is formed with a transparent electrode (ITO or IZO), and thenumber of the electrodes, the electrode interval and the layer, in whichthe electrode is formed, are changed.

[0298] In FIGS. 17A, 17B, 18A, 18B, 19A and 19B, the electrodes of therespective groups of electrodes have a zigzag form having plural crookedparts in the running direction thereof. One side on the crooked part hasan angle θ with respect to the direction of the image signal line DL,whereas the other side of the crooked part has an angle 180°-θ.

[0299] According to the configuration, the two regions (domains) havingreorientation states that are different from each other in direction areformed, and thus they compensates by each other inversion of coloringand gradation in oblique directions, whereby a wide viewing angle can beobtained.

[0300] In FIGS. 17A and 17B, it is constituted in such a manner that thedirection of the electric field between the pixel electrode and thecounter electrode is directed to the direction crossing the image signalline DL. FIG. 17A shows the case where the pixel electrode PX comprisessix pieces, and the counter electrode CT is formed in a solid form onthe whole pixel region.

[0301] In FIG. 17A, the electrode ST is connected to the counterelectrode and is extended outward to the boundary of the black matrix BM(shown by the outer dotted line in FIG. 17A) and inward to the innerdotted line.

[0302]FIG. 17B shows the case where the pixel electrode PX comprises sixpieces, and the counter electrode CT overlaps alternately the pixelelectrode and has a width that is larger than the pixel electrode. Incomparison to the case of FIG. 17A, the capacitance of the storagecapacitance can be made as small as 400 fF.

[0303] In FIGS. 18A, 18B, 19A and 19B, it is constituted in such amanner that the direction of the electric field between the pixelelectrode and the counter electrode is directed to the direction alongthe image signal line DL. In FIGS. 18A and 18B, the counter electrode CTis formed on the substantially whole pixel region. The electrode width,the number of the electrodes and the electrode interval are changedbetween FIG. 18A and FIG. 18B.

[0304] Specifically, the width of the pixel electrode PX is 5 μm in FIG.18A, whereas the width of the pixel electrode in FIG. 18B is 9 μm. Thenumber of the pixel electrode in one pixel is 30 in FIG. 18A.

[0305] The electrode interval is 5 μm in FIG. 18A, whereas it is 4 μm inFIG. 18B. In FIG. 18B, the transmittance is improved in comparison toFIG. 18A. FIGS. 18A, 18B, 19A and 19B contain an s-shape where the endof the pixel electrode is inverted up and down inside one pixel. This isbecause the auxiliary capacitance between the pixel electrode and thecounter electrode is made uniform in the direction of the scanningsignal line GL.

[0306]FIG. 19A shows the case where the pixel electrode PX has a widthof the pixel electrode of 5 μm and an interval to the adjacent pixelelectrode PX of 5 μm, and the counter electrode CT overlaps alternatelythe pixel electrode and has a width that is larger than the pixelelectrode PX.

[0307] In FIG. 19B, the pixel electrode PX has a width of 4 μm and aninterval to the adjacent pixel electrode PX of 4 μm. The opening ratioin FIG. 19B is improved in comparison to FIG. 19A. The constitution ofthe pixel in FIGS. 19A and 19B can reduce the auxiliary capacitance incomparison to the constitution of the pixel in FIGS. 18A and 18B.

[0308] It is understood from the foregoing examples that an activematrix liquid crystal display device causing less after image can beprovided.

[0309] As described in the foregoing, according to the invention, suchan active matrix liquid crystal display device can be provided in thatwhen a liquid crystal driving voltage wave having a direct currentvoltage overlaid is applied to a liquid crystal layer, a direct currentvoltage remaining in the liquid crystal layer after removing the applieddirect current voltage is removed to suppress an after image.

What is claimed is:
 1. An active matrix liquid crystal display devicecomprising a pair of substrates; a liquid crystal layer sandwiched bysaid pair of substrates; orientation films defining an orientationdirection of a liquid crystal molecule of said liquid crystal layer,said orientation films being arranged between said pair of substratesand said liquid crystal layer; and a pixel electrode and a counterelectrode applying a voltage to said liquid crystal layer, said liquidcrystal molecule of said liquid crystal layer having negative dielectricanisotropy, and said liquid crystal layer containing a dopant having adissociative group.
 2. An active matrix liquid crystal display device asclaimed in claim 1, wherein at least one electrode of said pixelelectrode and said counter electrode has an electrode width of from 1 μmto 15 μm and an electrode interval of from 1 to 10 μm, and one of saidpixel electrode and said counter electrode comprises a transparentelectrode.
 3. An active matrix liquid crystal display device as claimedin claim 2, wherein said transparent electrode comprises either ITO orIZO.
 4. An active matrix liquid crystal display device as claimed inclaim 1, wherein said pixel electrode and said counter electrode have azigzag form having plural crooked parts.
 5. An active matrix liquidcrystal display device as claimed in claim 4, wherein said devicecomprises thin film transistors at respective crossing parts of pluralimage signal lines and plural scanning signal lines, which are formed ina matrix form, and at least one pair of said pixel electrode and saidcounter electrode per one pixel formed with said respective thin filmtransistors, said pixel electrode and said counter electrode beingformed in the same direction as a direction, along which said scanningsignal lines are laid.
 6. An active matrix liquid crystal display deviceas claimed in claim 1, wherein said dopant contained in said liquidcrystal layer has a dissociative group only in a shorter axis directionof a molecule and has an alkyl group or an alkoxy group on both ends ofsaid shorter axis direction of a molecule, and is contained in saidliquid crystal layer in a range of from 100 ppm to 1,000 ppm.
 7. Anactive matrix liquid crystal display device as claimed in claim 6,wherein said dopant is a compound represented by the general formula(I):

wherein Y₁ represents any one of —COOH, —CONH₂, —NH₂, —OH, —NHR or —NR₂;Y₂ represents anyone of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; Y₃represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; Y₄represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; X₁represents any one of a single bond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—,—CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one of a singlebond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or—CH═CH—; A₁ represents any one of a single bond, a phenylene group or acyclohexylene group; A₂ represents any one of a single bond, a phenylenegroup or a cyclohexylene group; R₁ represents any one of an alkyl groupor an alkoxy group; and R₂ represents any one of an alkyl group or analkoxy group.
 8. An active matrix liquid crystal display device asclaimed in claim 6, wherein said dopant is a compound represented by thegeneral formula (II):

wherein Y₁ represents any one of —COOH, —CONH₂, —NH₂, —OH, —NHR or —NR₂;Y₂ represents anyone of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; X₁represents any one of single bond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—,—CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one of a singlebond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or—CH═CH—; A₁ represents any one of a single bond, a phenylene group or acyclohexylene group; A₂ represents any one of a single bond, a phenylenegroup or a cyclohexylene group; R₁ represents any one of an alkyl groupor an alkoxy group; and R₂ represents any one of an alkyl group or analkoxy group.
 9. An active matrix liquid crystal display devicecomprising a pair of substrates; a liquid crystal layer sandwiched bysaid pair of substrates; orientation films defining an orientationdirection of a liquid crystal molecule of said liquid crystal layer,said orientation films being arranged between said pair of substratesand said liquid crystal layer; and a pixel electrode and a counterelectrode applying a voltage to said liquid crystal layer, said liquidcrystal molecule of said liquid crystal layer having positive dielectricanisotropy, and said liquid crystal layer containing a dopant having adissociative group.
 10. An active matrix liquid crystal display deviceas claimed in claim 9, wherein said pixel electrode and said counterelectrode have a zigzag form having plural crooked parts.
 11. An activematrix liquid crystal display device as claimed in claim 10, whereinsaid device comprises said thin film transistors at respective crossingparts of plural image signal lines and plural scanning signal lines,which are formed in a matrix form, and at least one pair of said pixelelectrode and said counter electrode per one pixel formed at saidrespective crossing parts, said pixel electrode and said counterelectrode being formed in the same direction as a direction, along whichsaid scanning signal lines are laid.
 12. An active matrix liquid crystaldisplay device as claimed in claim 11, wherein at least one of saidpixel electrode and said counter electrode comprises either ITO or IZO.13. An active matrix liquid crystal display device as claimed in claim 1or 9, wherein said device comprises said scanning signal line, saidcounter electrode and a counter voltage signal line applying a countervoltage to said counter electrode formed on a side of said liquidcrystal layer of one substrate of said pair of substrates, a gateinsulating film formed on said scanning signal line, said counterelectrode and said counter voltage signal line, said pixel electrodeformed on said gate insulating film, a protective film formed on saidpixel electrode, and said orientation film formed between saidprotective film and said liquid crystal layer, and said liquid crystallayer has a specific resistance of from 1.0×10⁹ to 1.0×10¹² Ω·cm.
 14. Anactive matrix liquid crystal display device as claimed in claim 13,wherein said device comprises a color filter film formed on a side ofsaid liquid crystal layer of the other substrate of said pair ofsubstrates, a black matrix formed on said color filter film in a matrixform, and an overcoating film formed on said black matrix, and saidorientation film is formed between said overcoating film and said liquidcrystal layer.
 15. An active matrix liquid crystal display device asclaimed in claim 14, said passivation film comprises an inorganic filmusing a silicon oxide film or a silicon nitride film having a filmthickness of from 0.1 μm to 1 μm or an organic film comprising polyimidehaving a film thickness of from 2 μm to 3 μm.
 16. An active matrixliquid crystal display device as claimed in claim 1 or 9, wherein saidorientation film has a film thickness of from 20 nm to 300 nm.
 17. Anactive matrix liquid crystal display device as claimed in claim 16,wherein said orientation film mainly comprises polyimide.
 18. An activematrix liquid crystal display device as claimed in claim 15, wherein anelectrode is provided between said passivation film and said orientationfilm, and said electrode is in electrically contact with said pixelelectrode, said counter electrode, said scanning signal line, said imagesignal line or said counter voltage signal line.
 19. An active matrixliquid crystal display device as claimed in claim 18, wherein saidelectrode is in electrically contact with said pixel electrode, saidcounter electrode, said scanning signal line, said image signal line orsaid counter voltage signal line via a through hole.
 20. A liquidcrystal composition comprising from 100 ppm to 1,000 ppm of a dopanthaving a dissociative group only in a shorter axis direction of amolecule and having an alkyl group or an alkoxy group on both ends ofsaid shorter axis direction of a molecule.
 21. A liquid crystalcomposition as claimed in claim 20, wherein said dopant is a compoundrepresented by the general formula (I):

wherein Y₁ represents any one of —COOH, —CONH₂, —NH₂, —OH, —NHR or —NR₂;Y₂ represents anyone of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; Y₃represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; Y₄represents any one of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; X₁represents any one of a single bond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—,—CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one of a singlebond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or—CH═CH—; A₁ represents any one of a single bond, a phenylene group or acyclohexylene group; A₂ represents any one of a single bond, a phenylenegroup or a cyclohexylene group; R₁ represents any one of an alkyl groupor an alkoxy group; and R₂ represents any one of an alkyl group or analkoxy group.
 22. A liquid crystal composition as claimed in claim 20,wherein said dopant is a compound represented by the general formula(II):

wherein Y₁ represents any one of —COOH, —CONH₂, —NH₂, —OH, —NHR or —NR₂;Y₂ represents anyone of hydrogen, —F, —CN, —COOH, —CONH, —NH₂ or —OH; X₁represents any one of a single bond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—,—CH₂O—, —OCH₂—, —CH₂—CH₂— or —CH═CH—; X₂ represents any one of a singlebond, —CO—O—, —O—CO—, —COCH₂—, —CH₂—CO—, —CH₂O—, —OCH₂—, —CH₂—CH₂— or—CH═CH—; A₁ represents any one of a single bond, a phenylene group or acyclohexylene group; A₂ represents any one of a single bond, a phenylenegroup or a cyclohexylene group; R₁ represents any one of an alkyl groupor an alkoxy group; and R₂ represents any one of an alkyl group or analkoxy group.
 23. A liquid crystal composition as claimed in claim 20,wherein said liquid crystal composition has one of a difluorinatedbenzene structure, a dicyanobenzene structure and a monocyanocyclohexanestructure.
 24. An active matrix liquid crystal display device as claimedin claim 13, wherein said passivation film has a film thickness of from0.1 μm to 4 μm.